As has been reported by R. L. Kostelak in Lubrication, Volume 56, #4, 1970 (pg 49 et seq.), the principle of operation of the conventional differential in today's American automobile remains the same as the Pecqueur differential, invented in 1827. Although this "conventional differential" generally performs very satisfactorily, it has one serious shortcoming; namely, "stalling," which occurs when either rear wheel loses traction. Due to the kinematics of the conventional differential design, the driving torque is divided equally between the two rear wheels and is limited by the wheel with the least traction. Hence, when one wheel loses traction, the vehicle does not move.
To prevent this shortcoming, engineers have developed many ingenious ideas and mechanisms. Each manufacturer has his own descriptive name for his particular mechanism; for example, Chevrolet Positraction, Chrysler Sure-Grip, and Ford Traction-Lok. Generally, however, a differential incorporating one of these mechanisms is called a "locking" or "limited slip" or "controlled-slip" differential.
The limited slip differential used in the American passenger car is essentially the same as a conventional differential except for the incorporation of some form of friction members (e.g., clutch plates or friction cones). The Kostelak article describes the conventional differential and typical controlled-slip differentials. Another pertinent article is "Lubricants for Limited Slip Differentials" by John W. Allen, given at Fuels and Lubricants Meeting, Society of Automotive Engineers, Houston, Tex., Nov. 1-3, 1966.
U.S. Pat. No. 3,211,653 of O'Halloran discusses the problems of lubrication of a limited slip differential and reports that the addition of sulfurized sperm oil to such a lubricant produces severe noise on "sharp turn with braking." We have discovered that, contrary to the O'Halloran teachings, a cosulfurized blend of a triglyceride and a C.sub.2 -C.sub.128 monoolefin can be useful in lubrication of a limited slip differential.